Control of tanning drum temperature during tanning of animal hides

Abstract

The invention relates to a method of regulating an inside temperature of a tanning drum, during a dry tanning step of a tanning process of tanning a plurality of animal hides. The tanning drum comprises a center axis, a mechanical drive and an animal hide inlet. The mechanical drive is connected to an electric motor, wherein said electric 5 motor is configured to rotate said tanning drum via said mechanical drive. The inside temperature is regulated at least partly by first temperature regulating equipment and / or at least partly by second temperature regulating equipment. The first temperature regulating equipment includes a heating element, and the second temperature regulating equipment includes said electric motor and said mechanical drive providing 10 heat from rotation of said tanning drum when said tanning drum comprises said plurality of animal hides.

Description

CONTROL OF TANNING DRUM TEMPERATURE DURING TANNING OF ANIMALHIDESField of the invention

[0001] The present invention relates to a method of regulating an inside temperature of a tanning drum during a tanning step of a tanning process and to a tanning system implement such temperature control.Background of the invention

[0002] Known tanning processes typically use a large amount of water during the tanning step of a tanning process. Such large amount of water in a tanning drum is acting as a huge thermal energy storage making it difficult to perform temperature regulation of the inside temperature of the tanning drum. As a result, the hides tanned during a tanning process may be damaged and have a lower quality.Summary of the invention

[0003] The inventors have identified the above-mentioned problems and challenges related to regulation of the inside temperature of a tanning drum, and subsequently made the below-described invention which benefits from the possibility of using one of two heating source to regulate the inside temperature of a tanning drum, when the tanning drum comprises no or a very reduced amount of water.

[0004] The invention relates to a method of regulating an inside temperature of a tanning drum, during a tanning step of a tanning process of tanning a plurality of animal hides, wherein said tanning drum comprises a center axis, a mechanical drive and an animal hide inlet, wherein said mechanical drive is connected to an electric motor, wherein said electric motor is configured to rotate said tanning drum via said mechanical drive, wherein method comprise the step of regulating said inside temperature at least partly by first temperature regulating equipment and / or at least partly by second temperature regulating equipment, wherein said first temperatureregulating equipment includes a heating element, and wherein said second temperature regulating equipment includes said electric motor and said mechanical drive providing heat from rotation of said tanning drum when said tanning drum comprises said plurality of animal hides.

[0005] According to an advantageous embodiment of the invention, said tanning step is a dry tanning step.

[0006] Tanning should be understood as a part of the process of treating skins and hides (together referred to as hide) of animal to produce leather. The tanning process alters the protein structure of the hide, making it more durable and less susceptible to decomposition. Hence, the tanning process include a plurality of steps of which the tanning step is one step and during which the inside temperature of the tanning drum is regulated by the present invention. A dry tanning step may refer to a tanning step in which no tanning liquid is needed for the dissolution of a tanning agent. During a dry tanning step, a substance, such as water, in gaseous state may be introduced e.g. to regulate the temperature inside the tanning drum.

[0007] Hide should be understood as the natural skin and hair from an animal such as e.g. cattle. Hides may be a product from the cattle food industry and can be processed into leather. Part of this process is the tanning process the temperature of which is regulated according to the present invention.

[0008] The mechanical drive should be understood as a toothed wheel, pulley or similar which is fixed to the tanning drum and engaging with a chain, toothed wheel, belt or similar to converter rotation of an electric motor to rotation of the tanning drum. Note that the electric motor may be controlled by a motor drive.

[0009] The center axis should be understood as the geometric center of the tanning drum i.e., not necessarily a physical axis of the tanning drum. The center axis may be coincident with the centroid of the circular shape of the tanning drum when seen in an end view.

[0010] Using both first and second temperature regulating equipment i.e., heating from two different heating sources, is advantageous in that a reduction in power needed to increase the inside temperature of the tanning drum during the tanning step, is obtained compared to known tanning processes.

[0011] Further, since the tanning step is a dry (also referred to as Low Water Volumes Tanning Process) tanning step, the temperature inside the tanning drum can be regulated faster and more precise because there is added no liquid to the tanning drum prior to the tanning step. Hence, there is a reduced volume of tanning liquid for the tanning step that needs to be heated. It should be mentioned that the tanning drum may comprise liquid used during processing of the hides prior to the tanning step. Also, a small amount of liquid may be needed to dissolve components in addition to a tanning agent if such are required in the tanning step. Further, the hides may have absorbed liquid during pre-tanning steps / be wet and thereby contain liquid that may be found in the bottom of the tanning drum.

[0012] Further, the amount of tanning agent needed is reduced in that it does not have to be dissolved in a tanning liquid such as water.

[0013] First temperature regulating equipment should be understood as regulating temperature at least indirectly by use of a hearing element for heating up fluid in the tanning drum or heating up fluid outside the tanning drum prior to introducing the fluid into the tanning drum.

[0014] Second temperature regulating equipment should be understood as regulating temperature by friction between the animal hides / hides and drum wall when these are rotated in the tanning drum. This contribution to increase the temperature inside the tanning drum could be said to be free of charge in that rotation of the tanning drum is a necessary part of the tanning process. With this said, higher rotation speed may be needed to facilitate a heat generation compared to the operation speed needed for the tanning process if not heat was to be generated from friction between hides and inner drum surface. Such higher rotation speed may then lead to a minor increase in energyrequired to rotate the drum. When using certain tanning agents such as vegetable, heat generated by rotation of the drum may be sufficient to reach the desired temperature.

[0015] Because of the significant reduction of water needed in the tanning step, the temperature control according to the present invention is possible and facilitates a sufficiently precise temperature control and thereby a higher quality of the tanning. Further, a faster response time to temperature changes is advantageous. Further, the speed of reaching the desired temperature of the tanning step is increased leading to a better tanning process by fixing or binding the tanning agent to the animal hide. Thus, the temperature may be increased for chrome fixation and the pH may be increased for rise in shrinking temperature.

[0016] According to an advantageous embodiment of the invention, said tanning drum further comprises a temperature sensor.

[0017] A temperature sensor is advantageous in that a direct measurement of inside tanning drum temperature is provided and thereby it is possible to obtain a more precise temperature and faster response time for changes in temperature during the tanning step. Thereby, the risk is mitigated for a reaching a temperature, during the tanning step e.g., that is too high for a specific hide which may damage the hide.

[0018] According to an advantageous embodiment of the invention, said temperature regulation of said tanning step is automatically controlled by a controller based on a temperature measured by said temperature sensor.

[0019] Providing the temperature measurement from the temperature sensor to a controller is advantageous in that an automatic temperature control loop is thereby established based on which the controller is able to control injection of temperature regulated fluid into the tanning drum or regulating the rotation speed of the tanning drum and thereby regulated a temperature increase.

[0020] According to an advantageous embodiment of the invention, said tanning drum further comprises at least one, preferably at least two, most preferably at least three air release valves.

[0021] Two or three air release valves are advantageous in that during rotation of the tanning drum there will always be one that is in the upper half of the tanning drum / at or above the center axis of the tanning drum. In this way, one air release valve always provides a free passage from the interion of the tanning drum to the outside of the tanning drum when the tanning drum is rotating. Thus, pressure does not increase inside the tanning drum as fluid is introduced into the tanning drum.

[0022] According to an advantageous embodiment of the invention, said tanning drum comprises a fluid inlet valve controlling the inlet of fluid into said tanning drum.

[0023] The fluid inlet may be at the center axis of the tanning drum. The fluid may enter a fluid flow guide which may be referred to as a washboard. From the washboard, the fluid may enter a hide compartment HC of the tanning drum. A washboard may comprise two opposite ends fluidly connected through the center of the tanning drum. In each of the distal ends of the washboard a plurality of holes may be provided. These holes may act as a flow guide that distributes the fluid into the tanning drum. Distribution of the fluid is advantageous in that the hides inside the tanning drum are not directly in contact with a fluid or fluid in a gaseous form, at given temperature, that might damage said hides during said tanning process.

[0024] The fluid inlet valve may in principle be positioned at any position of the conduit from the fluid source / fluid heater to the inlet into the tanning drum.

[0025] The fluid inlet valve is advantageous in that it eases the control of input of a fluid such as water in gaseous form such as steam. Thus, the total amount of water introduced can be monitored and controlled, and excess use of water can be avoided. Excess water may further, increase the amount of tanning agent needed in the tanning step which thereby is avoided.

[0026] The terms steam and vapor may be used interchangeably. As used herein the term “steam” refers to a substance in gaseous state. The steam could stem from, e.g., an organic source, such as diethyl ether or water.

[0027] The fluid inlet valve may be implemented as a regulation valve, a solenoid vale, pneumatic valve or the like or a plurality of conduits having different orifices. The latter may lead to an additional level of control of how much water that is introduced in the tanning drum.

[0028] According to an advantageous embodiment of the invention, said tanning drum comprises a liquid content with no liquid surface inside said tanning drum.

[0029] A liquid surface should be understood as the surface of a liquid from which it is possible to measure a liquid collum. The liquid collum is thus measure from this surface to the lower most point of the tanning drum.

[0030] When the tanning drum is rotating, liquid in the tanning drum may follow the hides up and down and around inside the tanning drum due to its rotation. Thus, during rotation liquid inside the tanning drum may not gather and therefore there may be no visible liquid surface inside the tanning drum.

[0031] Further, the amount of the liquid inside the tanning drum may be so limited that even after half a second or after a few seconds such as after e.g. between 1 and 10 seconds of stand still of the tanning drum, the liquid inside the tanning drum, which is not comprised by the hides, still have not gathered in the bottom of the tanning drum. Hence, after such standstill period, of any natural number between e.g. 1 and 10 seconds, it may not be possible to measure a liquid level over 20cm, such as over 15cm, such as over 5cm or any natural numbers between 0cm and 25cm. This may at least be the case if the hides are removed from the tanning drum before measuring the liquid level.

[0032] According to an advantageous embodiment of the invention, said tanning drum comprises a liquid content with a liquid surface inside said tanning drum during said tanning step which is below said center axis.

[0033] As the tanning step of the present invention is a dry tanning step no tanning liquid is needed for the dissolution of the tanning agent. Thus, introduction of a fluid may be used only for temperature regulation. However, as mentioned, some carryover liquid (also simply referred to as liquid) from previous processes performed inside the tanning drum and contained in the hide may be present in the tanning drum during the tanning step. Preferably, the surface of this liquid (i.e. liquid not comprised by the hides) after a period of no rotation of the tanning drum is below the center axis. Such period of no rotation may be between 5 and 10 minutes and may be referred to as a settling time.

[0034] According to an advantageous embodiment of the invention, a distance from the surface of said liquid to said center axis during standstill of said tanning drum is at least 25cm, preferably at least 50cm, most preferably at least 100cm.

[0035] As the tanning drum comprises a plurality of hides, there may not be a liquid surface such as a horizontal liquid surface as such. However, it is still possible to determine an estimated liquid surface and that estimated liquid surface with hides in the tanning drum below the center axis. Preferably, the distance between this estimated liquid surface and the center axis is at least 100cm.

[0036] If the hides are removed from the tanning drum, the liquid surface will drop and the distance to the center axis will increase. Hence, if no estimated liquid surface can be determined, the hides can be removed from the tanning drum and a more precise distance from the then horizontal liquid surface to the center axis can be determined. Preferably, the distance between this estimated liquid surface and the center axis is at least 100cm.

[0037] Standstill should be understood as no rotation of the tanning drum for a time period sufficient for the liquid inside the tanning drum to settle with a substantially horizontal surface.

[0038] According to an advantageous embodiment of the invention, said tanning drum comprises a liquid content less than 10%, 20%, 25%, 30%, 40%, 50% by weight of said plurality of animal hides, when said plurality of animal hides are dry.

[0039] In relation to this specific way of measuring water content in the tanning drum it should be mentioned that it is a measure with reference to the liquid contained by the hide. Hence, the hides are considered dry when they e.g. are considered ready for use in leather production / considered a commodity. Accordingly, when it is stated that the tanning drum contains less than 50% of the weight of the dry hides, the weight of the liquid at the end of the tanning process is 50% less than the weight of the plurality of dry hides in the drum.

[0040] According to an advantageous embodiment of the invention, said tanning drum comprises a liquid content less than 10%, 20%, 25%, 30%, 40%, 50% by weight of said plurality of animal hides when said plurality of animal hides are soaked.

[0041] In relation to this specific way of measuring liquid content in the tanning drum it should be mentioned that it is a measure with reference to the liquid contained by the hide. Hence, when no more liquid can be contained by the hide, the hides are considered soaked. Accordingly, when it is stated that the tanning drum contains less than 50% of the weight of the soaked hides, the weight of the liquid at the end of the tanning process is 50% less than the weight of the plurality of soaked hides in the drum.

[0042] According to an advantageous embodiment of the invention, said tanning drum comprises a liquid content less than 110%, 120%, 130%, 140%, 150% of the liquid which is contained by said plurality of animal hides.

[0043] In relation to this specific way of measuring liquid content in the tanning drum it should be mentioned that it is a measure with reference to the liquid contained by the hide. Hence, when no more liquid can be contained by the hide, the liquid content in the tanning drum is 100%. Accordingly, when it is stated that the tanning drum contains less than 150% liquid, then the 100% is contained by the hide and another 50% of this amount is either added during the tanning process and / or is a carryover from a previous step in the preparation of the hide.

[0044] The percentages are made with reference to the water content in the hides. The water content in the hides cannot be more than 100%. The additional water may e.g. origin from carryover water from pickle bath (e.g. between 10% and 40%, ideally less than 10%), 2% dilution water and maybe a minor contribution from steam inlet.

[0045] According to an advantageous embodiment of the invention, an amount of added liquid during said tanning step is less than the amount of liquid present inside said tanning drum when starting said tanning step.

[0046] When the liquid is used to increase or decrease the temperature it may be introduced in gaseous form such as steam or as an aerosol. Introducing the fluid this way is advantageous in that a minimum of fluid is needed to obtain the desired regulation of temperature.

[0047] A common advantage of the above ways of defining a limited amount of water content in the tanning drum is that it reduces the amount of water used for the tanning step. Thus, reducing the amount of water reduces the amount of tanning agent needed, which leads to a process that has a reduced environmental impact. Additionally, the amount of wastewater is lowered which means that disposal of a lower volume of said wastewater is needed, which further reduces the environmental impact of the tanning step.

[0048] Common for all the above ways of defining the liquid content in the tanning drum is that the amount of liquid is measured when the tanning step is terminated. Theamount of liquid may partly be carryover from previous steps in the hide preparations and partly liquid added during the tanning step.

[0049] Common for all the above ways of defining the liquid content in the tanning drum it should be mentioned that the liquid contained or added to the tanning drum during the tanning step is used for regulating the inside temperature of the tanning drum (up og down).

[0050] Common for all the above ways of defining the liquid content in the tanning drum it should be noted that the liquid added to the tanning drum may be water, thus, the term liquid may in this document in this context be replaced with the term water.

[0051] According to an advantageous embodiment of the invention, said plurality of animal hides comprises a liquid content according to the liquid retention capacity.

[0052] According to an advantageous embodiment of the invention, said plurality of animal hides comprises a water content exceeding the water retention capacity.

[0053] As mentioned above, the term “soaked” refers to a state where the hides retain an amount of water, according to the maximum water retention capacity. The maximum water retention capacity may vary depending on the species of animals where the animal hide is derived from.

[0054] As used herein the term “maximum water retention capacity” refers to an amount of water that can be bound to a hide. Thus, water retention capacity does not refer to the amount of water that can drip off a hide directly after soaking.

[0055] Additionally, the hides can comprise an excess of water, exceeding the maximum water retention capacity. The excess of water, that exceeds the maximum water retention capacity can derive from a direct transfer from a soaking container in which a pre-tanning step is performed to a tanning drum or alternatively a noncomplete draining of the drum in which a pre-tanning steps is performed. Thus, “exceeding the maximum water retention capacity” is a result of not letting the hidesdrip off before the tanning process or none-complete draining. This excess water is also sometimes referred to as carryover water.

[0056] Moreover, soaking of the hides may also arise as a result of when the animal hides are pickled. Thus, the hides may be acidic prior to the tanning step. The animal hides to be tanned according to the present invention may typically be pickled animal hides.

[0057] According to an advantageous embodiment of the invention, a fluid is added to the interior of said tanning drum during said tanning step.

[0058] As used herein the term “fluid” refers to a liquid state or a gaseous state of e.g. water that may be introduced into the tanning drum in one of these forms, preferably gaseous in the form of steam, to regulated temperature, preferably increase temperature.. The fluid can possess different physical and chemical properties. Thus, the term may e.g., refer to organic solvents, inorganic solvents or water in either liquid or gaseous state.

[0059] Providing fluid during the tanning step may be advantageous for adjusting or optimizing the tanning of the hides e.g. by introducing tanning agents to the inside of the tanning drum via the fluid or by using a tempered fluid as a temperature regulating agent. Hence, the temperature of the fluid may be higher or lower than the temperature inside the tanning drum and thus introduction of the fluid may regulate the temperature inside the tanning drum up or down.

[0060] Using fluids in gaseous form may further be advantageous in that it can reduce the amount of fluid needed to reach certain temperatures which are optimal for the tanning. Thus, the amount of fluid used can be further reduced, which further decreases the amount of wastewater, and in turn decreases the environmental impact of the process.

[0061] According to an advantageous embodiment of the invention, said fluid is introduced into said tanning drum when said tanning drum is rotating.

[0062] This is advantageous in that it has the effect that the tanning is made uniform to all hides when all hides are continuously changing position in the tanning drum due to the rotation.

[0063] According to an advantageous embodiment of the invention, said fluid is added from a first or from a second fluid source.

[0064] This is advantageous in that it has the effect, that fluid of two different temperatures and / or two different types can be introduced into the tanning drum. Accordingly, if temperature is to be increased fluid from one source may be introduced and if temperature is to be decreased, fluid from the second source may be introduced. Flow of fluid from the two sources may be controlled by a plurality of valves and thus only one fluid inlet may be needed into the tanning drum for fluids from both sources.

[0065] According to an advantageous embodiment of the invention, said fluid is a tanning liquid.

[0066] As used herein the term “tanning liquid” refers to a fluid that comprises tanning agents or pH regulating agents or a combination thereof. Thus, a tanning liquid may be a mixture of chemicals and fluid such as water. It should be mentioned that a third fluid source may be used with a third fluid inlet to the drum. This may be needed if tanning agent or additional components needed during the tanning step is to be introduced.

[0067] According to an advantageous embodiment of the invention, said fluid is steam, preferably water steam.

[0068] According to an advantageous embodiment of the invention, wherein at least 50%, preferably at least 25%, most preferably at least 10% of the total injected fluid at the end of said tanning step origins from steam.

[0069] Using steam is advantageous in that in this way the maximum heat capacity of the fluid that is introduced into said tanning drum is utilized. The fluid introduced may be steam from / of water (H2O).

[0070] According to an advantageous embodiment of the invention, said fluid is introduced in discontinued time periods during said tanning step.

[0071] The injection or introduction of fluid is typically from 3-5 seconds to several minutes to hours. Depending on the temperature difference between the fluid and the temperature inside the tanning drum, the inside temperature may be regulated up or down with e.g. 0-3 degrees per hour. This temperature increase is mainly facilitated by injection of fluid but may be supported by the heat generated from rotation of the drum. Thus, it is not unlikely, that the temperature is increased, by introduction of fluid, for 10, 15, 20 or more minutes to obtain a desired tanning temperature, if the starting temperature is much lower than (e.g. between 10 and 25 degrees below) the desired temperature of the tanning step.

[0072] According to an advantageous embodiment of the invention, said discontinued time periods are present during a tanning part of said tanning step.

[0073] The tanning step starts with a mixing and distributing part at ambient temperature which has a duration e.g. between 4 and 12 hours. The tanning step ends with a tanning part at a specific temperature which is typically above ambient temperature which as a duration e.g. between 6 and 8 hours. Thus, it is during the tanning part, the temperature regulation of the present invention is most relevant.

[0074] According to an advantageous embodiment of the invention, a first time period of said discontinued time periods is between 5 and 60 minutes, such as between 5 and 45 minutes, such as between 5 and 30 minutes.

[0075] The time periods during which fluid is introduced into the tanning drum in the beginning of the tanning part of the tanning step is longest. This is especially true when the temperature inside the tanning drum is to be increased from ambienttemperature to a desired temperature. Then a flow of hot fluid may continuously be introduced for more than e.g. five minutes and until the measured temperature is as desired.

[0076] According to an advantageous embodiment of the invention, a last time period of said discontinued time periods is between 1 second and 1 minute, preferably between 2 second and 30seconds, most preferably between 3 seconds and 15 seconds.

[0077] The time periods during which fluid is introduced into the tanning drum towards the end of the tanning part of the tanning step is shortest. This is because the desired temperature is reached and only needs to be maintained which requires a less introduction of tempered fluid.

[0078] According to an advantageous embodiment of the invention, wherein said introduction of fluid is continuously introduced alternatingly between a temperature maintaining flow and a temperature increasing flow.

[0079] A continuous introduction of fluid such as steam may be introduced where the flow of steam such as the volume of steam per time unit is varied to obtain the temperature regulation. Accordingly, steam may be continuously introduced into the drum to maintain a desired temperature. However, if the temperature has to be increased, the flow of fluid into the drum need to be increased. Similarly, when the upper limit for temperature is reached, the flow has to stop. Accordingly, the discontinued introduction of fluid may be understood a pulses of flow from a first level of flow to second level of flow. Where the first level of flow is a temperature maintaining flow and the second level of flow is a temperature increasing flow. The second level of flow is determined by the temperature increase and the time to reach this temperature increase. During a temperature maintaining period a temperature maintaining flow of fluid is provided introducing a volume e.g. of steam per time unit which ensure to maintain a temperature between an upper and a lower threshold. During a temperature increasing period a temperature increasing flow of fluid isprovided introducing a volume e.g. of steam per time unit which is higher than during the temperature maintaining period.

[0080] It should be mentioned that by the inlet of X amount of steam the temperature in the drum will be increased with X degree of Celsius per hour. Accordingly, the desired temperature may be obtained e.g. by fine tuning the amount of steam inlet or the time the desired temperature could be reached.

[0081] The volume and time unit may be depending on type of hides to be tanned and thus determine individually for a particular tanning process.

[0082] According to an advantageous embodiment of the invention, said inside temperature is controlled to be between 20-55 degree Celsius.

[0083] Temperature regulation is advantageous in that the tanning step may be carried out in different climates. Thus, in colder climates it could be necessary to increase the temperature prior to the tanning step. In warmer climates, it may be necessary to decrease temperature inside the tanning drum prior to starting the tanning step. Ultimately, could the regulation of temperature prior to the tanning process, affect the outcome and quality of said tanning process. Further, the temperature control is advantageous in that different types of hides is tanned at different temperatures and / or the tanning step may include steps carried out at different temperatures.

[0084] According to an advantageous embodiment of the invention, said controller is decreasing said inside temperature by introducing said fluid when said fluid has a temperature which is below said measured temperature inside said tanning drum.

[0085] The controller may control a valve allowing a flow of e.g. air or aerosol passing through / by a cooling system and into the tanning drum and thereby automatically control / decrease the inside temperature based on input from the temperature sensor.

[0086] It is advantageous to be able to decrease the temperature inside the tanning container especially when said tanning drum is physically located in an ambient temperature that is substantially equal to or higher than the desired temperature for the tanning process.

[0087] According to an advantageous embodiment of the invention, said temperature of said fluid is controlled by a cooling system fluidly connected to said tanning drum.

[0088] On way of reducing the temperature of the fluid to be introduced into the tanning drum is by passing it through a heat exchanger of a cooling system. Such cooling system may be a standard cooling system e.g. with a compressor, condenser, expansion valve and evaporator / heat exchanger as known in the art. The introduction may be controlled by the controller via control of one or more valves in a conduit system between the cooling system and the tanning drum.

[0089] The controller may also control the cooling system such as the compressor and expansion valve.

[0090] According to an advantageous embodiment of the invention, said fluid having a temperature below said measured temperature is introduced into said tanning drum in a separate conduit.

[0091] A separated conduit system may be a conduit which is different form the conduit via which the temperature increasing fluid is introduced to the tanning drum.

[0092] According to an advantageous embodiment of the invention, said measured temperature inside said drum is controlled by a cooling system regulating a temperature of a cooling fluid circulated in a void between a second and a first wall of said drum.

[0093] This is advantageous in that the temperature inside the tanning drum may at least partly be controlled by such cooling fluid. Thus, the temperature inside the tanning drum may be controlled by this cooling fluid, by the additional fluid introducedinto the tanning drum or by a combination thereof. It should be mentioned that temperature regulation may also include increasing temperature, in this situation the cooling fluid would be a heating fluid although the fluid is the same. In some embodiments, when utilizing a heating fluid in the void between a second and a first wall, the heating fluid may be utilized instead of a heating element. In different embodiments, when utilizing a heating fluid in the void between a second and a first wall, the heating fluid may be utilized combined with a heating element.

[0094] The cooling or temperature regulating system may facilitate that a cooling fluid may be circulated in the void between the first and second wall of a double walled drum. Hence, by regulating the temperature of the cooling fluid (e.g. via a heat exchanger of the cooling system), the temperature inside the drum can be regulated (up or down) without getting in direct contact with the hides, opening the drum or in other ways interfering with the tanning process. As an alternative, electric heating or cooling systems may be used.

[0095] According to an advantageous embodiment of the invention, said controller is increasing said inside temperature by introducing said fluid when said fluid has a temperature which is above said measured temperature inside said tanning drum.

[0096] The controller may control a valve allowing a fluid flow such as e.g. a flow of air, water or aerosol passing through / by a heater / first temperature regulating equipment comprising a heating element and into the tanning drum and thereby automatically, control / increase the inside temperature based on input from the temperature sensor.

[0097] Typically, the temperature inside the tanning drum is controlled to be in the range of 20°C and 45°C. Accordingly, the fluid may be higher or lower than the ambient temperature.

[0098] According to an advantageous embodiment of the invention, said fluid is introduced into a hide compartment of said tanning drum above said center axis.

[0099] Advantageous in that it eases the monitorization of temperature, and avoid reaching too high temperatures, that could damage the hides, that are processed withing the tanning drum. Additionally, providing an inlet makes up a further advantage in that there is no need to mix chemicals in a solution beforehand. Thus, the total amount of water can be monitored, and excess use of water can be avoided.

[0100] Further, introducing said fluid, when said fluid e.g. is a hot steam, above the center axis reduces the risk of a hide is exposed directly to the steam which may damage the hide. Preferably, the fluid is introduced into the hide compartment behind a hide shovel (with respect to direction of rotation) which ensures mixing of hides with tanning agent during rotation of the tanning drum.

[0101] According to an advantageous embodiment of the invention, said heating element is heating up said fluid outside of said tanning drum which fluid is subsequently introduced into said tanning drum via a conduit.

[0102] Heating up fluid outside the tanning drum is advantageous in that standard off-the-shelf heating systems can be used.

[0103] According to an advantageous embodiment of the invention, said heated fluid is introduced into said tanning drum in gaseous form.

[0104] Introducing the heated fluid e.g. as a hot steam of water, is advantageous in that it has the effect that the amount of fluid needed to regulate the temperature upwards is reduced, compared to the use of a fluid in its liquid form. This is true both if such liquid is heated inside or outside of the tanning drum.

[0105] A reduction of fluid inside the tanning drum is advantageous in that dosing a tanning agent correctly is easier in that a larger part of the tanning agent is absorbed by the animal hides compared to tanning in larger amounts of liquid inside the tanning drum where some tanning agent will remain in wastewater after the tanning process.

[0106] A larger amount of liquid inside the tanning drum may be understood as liquid having a surface which is at or above the center axis, such as at or above a distance of 10cm below the center axis, such as at or above a distance of 50cm below the center axis.

[0107] According to an advantageous embodiment of the invention, rotation of said tanning drum is control by said controller controlling frequency and voltage of power supply to said electric motor.

[0108] Controlling power supply to a motor may be performed by a motor drive connecting a power source to the motor. A motor drive may be understood as a variable frequency drive for controlling the rotations speed of the electric motor. Alternatively, a simple start and stop control of a current path to a motor may also be considered a power delivery control to an electric motor.

[0109] According to an advantageous embodiment of the invention, an increase of the rotation speed of a motor axis of said electric motor is contributing to increasing said inside temperature of said tanning drum.

[0110] According to an advantageous embodiment of the invention, said electric motor is a variable speed motor,

[0111] In the same way, the contribution to the temperature regulation from the second temperature regulating equipment i.e. from rotation of the tanning drum may be reduced by reducing the rotation speed of the tanning drum.

[0112] It should be mentioned that rotations speeds of the tanning drum between 0,5 rounds per minute (RPM; Rounds Per Minute) and 10 RPM has proven to be suitable rotations speeds for a tanning process according to the present invention.

[0113] Using temperature regulation by rotation may further be advantageous, in that rotation may induce friction of the surfaces of the hides inside the tanning drum. The friction induced by rotation may result in a change of temperature. Thus, thetemperature can be adjusted according to said rotation speed, enabling an additional way to alter the temperature. Even further, friction can be used to achieve specific temperatures for the tanning process. Thus, the need for heating from other sources could be reduced. The other sources could e.g., be warm fluids or vapor. Ultimately, when using some types of tanning agents, this could result in a further reduction of wastewater (no fluid to increase temperature may be needed), reducing the environmental impact of the tanning process.

[0114] Using a restricted amount of water or no water at all may further be advantageous. The restricted amount of water inside the tanning drum would affect the amount of friction between the animal hides. Thus, if the water content is too great inside the tanning drum, the heat from friction could be lost.

[0115] According to an advantageous embodiment of the invention, said second temperature regulating equipment is provided when said liquid surface is less than 10cm from the bottom of said tanning drum, such as less than 5cm from the bottom of said tanning drum.

[0116] The less liquid present in the tanning drum, the higher contribution to a heating process of the inside temperature of the tanning drum is possible to obtain from friction. Thus, it is advantageous only to have a humidity inside the tanning drum that does not condense and thereby establish a volume of liquid in the bottom of the tanning drum that has a measurable / visible liquid surface immediately after stopping rotation of the tanning drum such as withing 10-30 seconds from stopping rotation. Provided may be understood as applied, come into play or being used to regulated temperature inside the tanning drum.

[0117] It should be mentioned, that contributing to the increase of temperature inside the drum is an increase of speed or just by time and friction the Temperature can increase. This is at least true when the drum comprise a gearbox drive rather than a blet drive. The adjustment of speed could be done automatically based on experience such as 2 Hours Speed 2 RPM, 2 Hours Speed 3 RPM etc. but also manually based onthe achieved temperature increase to increase the RPM (Rotation per Minute / Speed) more when needed to get a higher temp.

[0118] According to an advantageous embodiment of the invention, said automatically controlled temperature regulation comprises the following steps: during rotation of said tanning drum, detect a current temperature inside the tanning drum, if said current temperature is below a lower threshold temperature, inject a water steam into said tanning drum via said fluid inlet, to increase said current temperature, and if said current temperature is between said lower threshold temperature and a first upper threshold temperature, continue rotation of said tanning drum without injecting fluid into said tanning drum.

[0119] According to an advantageous embodiment of the invention, said automatic control further comprises the step of if said current temperature is above a second upper threshold temperature, inject fluid into said tanning drum via said fluid inlet, to decrease said current temperature.

[0120] This way of controlling is advantageous in that both a decrease and an increase of temperature inside the tanning drum can be provided and thus it is easier to maintain the inside temperature of the tanning drum between the lower and the first threshold temperatures. A more precise temperature control leads to a better tanning and thereby better quality of the tanned hide. Further, the risk of damaging hides due to too high temperature is reduced in that cooling of the tanning drum is possible.

[0121] According to an advantageous embodiment of the invention, said fluid inlet is closed during detection of said current temperature.

[0122] This is advantageous in that a flow inside the drum may affect the readings from the temperature sensor which therefore may not measure accurate temperature.

[0123] According to an advantageous embodiment of the invention, said plurality of animal hides is washed in a washing process after said tanning step.

[0124] The washing is particularly advantageous when tanning according to the present invention i.e., without water / with a very reduced amount of water. There may be tanning agent not absorbed and fibers such as hair from the hide which hare not removed from the tanning drum by draining as is the case with known “wet” tanning processes.

[0125] A washing process is advantageous in that it helps removal of excess tanning agents, such as chrome salts in chrome tanning or vegetable tannins in vegetable tanning. Thus, preventing excess tanning agents, can avoid formation of stiff or brittle leather. Accordingly, the washing process includes washing, dragging through, rotating, etc. the hides in a container with water.

[0126] According to an advantageous embodiment of the invention, said washing process is carried out outside said tanning drum in a washing container comprising a fiber filtration filter.

[0127] An advantage of a fiber filtration filter is that, the fluid used for rinsing is continuously filtered and can therefore be used for rinsing / washing more hides before it need to be changed. Thus, the environmental impact of this process is further reduced. The amount of fibers in the tanning drum after a tanning step according to the present invention is higher compared to a traditional wet tanning process. This is because the no water (or a very reduced amount of water) is present in the tanning drum and thus no fibres are removed during drainage. If removal is required before the sammying process, which may be in case that high quality leather is made, the fibres need to be removed during a washing process between the tanning and sammying processes.

[0128] According to an advantageous embodiment of the invention, said animal hide comprise bovine hide, cattle hide, cow hide, or calf hide.

[0129] According to an advantageous embodiment of the invention, pressure inside said tanning drum during said tanning process is within a range of 0.7-1.3 atmospheric pressure such as 0.9-1.1 atmospheric pressure.

[0130] In an aspect, the invention relates to an animal hide tanning system configured for tanning a plurality of animal hides, said tanning system comprising: a tanning drum, said tanning drum comprising a center axis, a mechanical drive and an animal hide inlet, wherein said mechanical drive is connected to an electric motor, wherein said electric motor is configured to rotate said tanning drum via said mechanical drive, a temperature control system, said temperature control system comprises a temperature sensor, a first temperature regulating equipment, a second temperature regulating equipment and a temperature controller, wherein said temperature controller is configured for regulating an inside temperature of said tanning drum, during a process of tanning a plurality of animal hides by regulating said inside temperature at least partly by said first temperature regulating equipment and / or at least partly by said second temperature regulating equipment, wherein said first temperature regulating equipment comprises a heating element, and wherein said second temperature regulating equipment comprises said tanning drum comprising said plurality of animal hides and configured for being rotated.

[0131] Note that the heating element may be an electrical heating element and note that heat from the tanning drum may be friction heat generated by rotating the tanning drum comprising a plurality of animal hides in a reduced / limited amount of water. As mentioned above, the temperature inside the tanning drum may during a tanning step such as a dry tanning step be regulated at least partly be introducing a substance, such as water, in gaseous state. According to an advantageous embodiment of the invention, said tanning system further comprises a cooling system configured for cooling a fluid wherein said cooling is configured for being introduced into said tanning drum via a conduit.

[0132] This is advantageous in that the system may then also be able to reduce the inside temperature of the tanning drum.

[0133] According to an advantageous embodiment of the invention, said fluid is introduced in discontinued time periods during said tanning step.

[0134] According to an advantageous embodiment of the invention, said discontinued time periods are present during a tanning part of said tanning step (TAN).

[0135] According to an advantageous embodiment of the invention, a first time period of said discontinued time periods is between 5 and 60 minutes, such as between 5 and 45 minutes, such as between 5 and 30 minutes.

[0136] According to an advantageous embodiment of the invention, the system according to any of the claims 47-52 is regulating the inside temperature of said tanning drum by implementing the method of any of the claims 1-46.The drawings

[0137] Various embodiments of the invention will in the following be described with reference to the drawings where: fig. 1 illustrates the steps of a tanning process, fig. 2 illustrates a tanning drum and wash container used for a tanning step and a washing step according to an embodiment, fig. 3 illustrates temperature regulation equipment according to an embodiment, and fig. 4 illustrates relationship between discontinued introduction of fluid to the tanning drum and inside temperature of the tanning drum.Detailed description

[0138] Fig. 1 illustrates the steps of pre-tanning, tanning and post tanning of animal hides. Several steps are needed in order to prepare the hides for the tanning process of the tanning step TAN and ultimately obtaining the finished leather LE. At least some of these steps are described briefly below and it should be noted that one or more steps are optional depending on the specific hide, process and end product. Preparing or pretanning PRET raw hides RH begins by curing CUR the raw hides RH with salt to prevent putrefaction of the collagen from bacterial growth during the time from procuring the hide to when its processed. Curing CUR removes water from the hides and bacterial are unable to grow. Curing CUR may depend on if hides are salted or fresh be followed by a desalting DES.

[0139] The animal hides AH are then soaked SO A in clean water that may contain additives such as e.g. degreasing, soda, enzymes, and / or bactericides in a soaking step, where the salt left from curing is removed and the moisture in the hides is increased. Soaking takes place at pH between 8 and 10.

[0140] In the liming step LIM, sulphur compounds as well as lime, enzymes and / or degreaser may be added to remove the hair of the hide. The proteins are hydrolysed, i.e. rendered water soluble, at a high pH such as e.g. 12 to 13, and washed off. This process may also be known as hide opening up (i.e. opening up the skin and liberation of tanning-active groups) of the collagen fibre texture and partial saponification of the natural grease.

[0141] After liming, fleshing FLE is conducted and during the fleshing step, remnants of tissue, flesh and fat are removed using sharp bladed rolls. It should be noted that green fleshing and splitting may be possible after the soaking and before the liming LIM processes. To obtain uniformly thick leather in a desired thickness, the hide can be split SPL. The untanned leather may also be known as a pelt. A pelt has a water content of 60% - 80% and the dry matter contains approximately 98% collagen.

[0142] Additionally, the fleshing may also be carried out before the liming process.

[0143] The swelling induced in the liming process, by the high alkalinity, has to be eliminated before tanning and by a deliming process, the pH of the collagen is reduced. During deliming DEL the calcium hydroxide in the hide is removed by adding weak organic acids, e.g. aliphatic or aromatic dicarboxylic acids such as e.g. sulphophthalic acid or by adding weakly inorganic salts, such as e.g. ammonium sulphate, ammonium chloride or polyphosphates. In deliming, the calcium hydroxide in the hide is removed.

[0144] Optionally and depended on the end use of the leather LE, the hide may be treated with enzymes to soften them, in a process called bating BAT. Bating is performed in a somewhat heated float, i.e. at 30 to 35 degree Celsius.

[0145] Pickling PIC is the process where hides and skins are treated first with common salt (sodium chloride) and then with sulfuric acid, in the case of a mineral tanning. This is done to bring down the pH of collagen to facilitate the penetration of tanning agent. The bating process may take between 45 minutes to 6 hours at pH of 7- 9 and the pickling process may take approximately 5 to 12 hours at pH 2.8 to 5, such as 2.8 to 3.2 for a standard pickle process.

[0146] The hide obtained after bating BAT and pickling is fully saturated with aqueous solution and is known as a pickled pelt.

[0147] At his point what can be referred to as pre-tanning PRET ends. Hereafter, the actual tanning is carried out in the tanning step TAN, conventionally taking 10 to 20 hours and often carried out in rolling tanning drums TD.

[0148] The tanning TAN of the hides AH may be carried out in a tanning solution the main component of which is the tanning agent. The tanning agent may be dissolved in the water remaining in the tanning drum as a carry-over from the previous steps or from water retained in the hides. Hence, tanning agent in a powder form may be introduced into the tanning drum with no additional water, the dosing of tanning agent is made by weight of the hides. This weight may be determined during or after the laststep prior to the tanning step which may be the pickling step. It should be noted, that if additional components are needed in addition to the tanning agent, then these additional components may require to be dissolved in water. The amount of water needed for this may be in the range of 1% of the total amount of water added during in the tanning step. In fact, to ensure a best possible distribution hereof in the drum such additional components may be introduced via a fluid inlet at the axis of the drum. This fluid inlet may be different from the fluid inlet that is used to inject the temperature regulating fluid.

[0149] Thus, the tanning solution may contain e.g. salt, formic acid, sulphuric acid, sodium bicarbonate and may have additional compounds. During tanning, the bonding-capable groups on the collagen undergo crosslinking with the tanning agents. The pH may be raised to values between 3.6 to 4.2 e.g. by addition of alkali or by using a self-basifying tanning agent.

[0150] As an example, the basification may be performed by the introduction of 0.4- 0.6% (36.5 kg) Feliderm MgO into the tanning that may be added in several steps, where the basification process may be run for eight hours.to bind the tanning agent in the animal hides, e.g. in case of Chromosal B is being used as a tanning agent.

[0151] Tanning agents may be any suitable tanning agent for tanning animal hides including but not limited to chromium sulphate and its derivates, vegetable extracts, glutardialdehyde, fatty oils in particular and other mineral salts based on aluminium, zirconium, titanium, iron, silicates, etc. and synthetic tanning agents based on acrylics, acrylic copolymers, triazine, polyphenols, polysulphonic acids and condensates thereof, etc.

[0152] The tanning agent may further comprise additional components such as Fungicides (Busan 1280), or other additives that may provide additional qualities to the tanned leather or the tanning process. The tanning agent may include other additives such as e.g. electrolyte stable fatliquors, cationic / fatliquor or slippery agents. The tanning agent may be provided to the container in any form, where eachcomponent is introduced separately or in a mixture, which may be in solid or liquid form. Examples of commercially available tanning agents are Chromosomal B and Baychrome A.

[0153] Other compounds may also be used during the tanning process and these compounds may be sodium sulphide, sodium hydroxide, sodium hydrosulfite, arsenic sulphide, calcium hydrosulfide, dimethyl amine and sodium sulphydrate. Biocides such as e.g. pentachlorophenol may also be added to prevent bacterial growth.

[0154] After the tanning step TAN, what can be referred to as post-tanning steps may be applied. A first post-tanning POSTT step is washing WAS. This step between the tanning TAN and the sammying SAM steps is of particular importance for the present invention in that the tanning step TAN is made with a very limited amount of water. Because the tanning of the present invention is made with a reduced amount of water and thereby reduced amount of waste water more fibers leave the tanning drum with the hides compared to conventional “wef’-tanning. In such conventional tanning, fibers from the hides may at least partly be washed off by / removed from the hides with the wastewater.

[0155] Thus, the washing WAS step after a tanning step TAN according to the present invention require more frequent replacement of the water in the washing container WC due to the higher amount of fibers. Thus, the water saved by the inventive heating at the tanning step TAN could be said to be used or at least part of it used in the subsequent washing process thereby reducing the effect of the inventive heating at the tanning step TAN. However, to reduce the need for replacement of the water the washing container WC is modified as described in relation to fig. 2.

[0156] The next step is the sammying SAM, sammying SAM is the process that reduces the humidity to 45-65% by passing the hide through e.g. rollers. Splitting is the process, where leather can be passed through a splitting machine, which slices thicker leather into two layers. The layer without a grain surface can be turned into suede or it can have an artificial grain surface applied. A uniform thickness can beachieved by shaving the leather on the non-grain side using a machine with helical (spiral shaped) blades mounted on a rotating cylinder.

[0157] According to embodiments of the invention, the animal hide may be sammed. The sammying of the animal hide may assist in cleaning the animal hide, where the sammying removes fibres from the animal hide or absorbs grease. The sammying machines absorb the grease and humidity from the hide during the wet process in tanneries, either wet blue, wet white or vegetable.

[0158] A step of neutralization NEU may be applied that removes any residual chemicals and prepares the animal hides for further processing. As an example, this could be deacidification, where remaining acids are removed, thus, restoring pH to neutral. Additional tanning or retanning RET may be applied to add more tanning agent such as e.g. chrome, to provide the hide with optimal properties required in the finished leather. Then the dyeing DYE of leather into a wide variety of colours play an important role for aesthetic appearances and an important part in meeting fashion requirements. Fatliquoring FAT is the step of introducing oil to the animal hides to lubricate the fibers for keeping the leather flexible and soft.

[0159] The post tanning process involves neutralization of the cationic charge of the chrome tanned animal hides by elevating the pH of the animal hides to 4.5-6.5

[0160] Several finishing steps FIN may then follow, such as e.g. conditioning, staking, dry drumming / milling, buffing, brushing, surface coating etc. (not shown)

[0161] Fig. 2 illustrates a tanning drum TD in an end view which is used during the tanning stem TAN and the washing container WC that is used to wash the hides after the tanning step TAN. Additionally, the tanning drum TD comprises air release valves ARV, to relieve pressure.

[0162] The outer end of the drum TD is removed so that it is possible to look inside the tanning drum TD. Inside the tanning drum, four shovels SH are illustrated. Theseshovels SH ensure that the hides AH are lifted up and dropped again and thereby mixed during rotation of the drum TD.

[0163] The drum TD is illustrated without any water but the water contained by the hides (which is also not illustrated). If the hides all retain their maximum capacity, according to this document the amount of water in the drum is 100%. The present invention teach a method of regulation control which is suitable for tanning steps TAN in which the total amount of water, i.e. water in addition to the 100% water retained by the hides, has a water level below the center axis CA.

[0164] In the illustrated embodiment, at the center axis CA at least one fluid inlet is located. This inlet is fluidly connecting the inside of the Tanning drum TD (also sometimes called the hide compartment) with the first temperature regulation equipment 1TRE. The first temperature regulation equipment 1TRE comprises a fluid supply FS and a heating element HE. These elements are connected by a conduit CO. A controller CON is controlling status of valves VA in the conduits CO and is controlling the heating element HE. Thereby, the controller CON is controlling a flow of fluid and the temperature of the fluid injected into the tanning drum TD. As mentioned elsewhere in this document, preferably the fluid is a water steam.

[0165] The fluid is injected into a washboard inlet WBI which is fluidly connecting the fluid inlet with the washboard WB at the outermost periphery of the inside hide compartment HC of the tanning drum TD. The washboard is a perforated ring that allows distribution of the fluid inside the drum. In this way, the fluid is not introduced directly into the drum with the risk of damaging a hide. Typically, as the fluid is a hot steam is will take the washboard inlet WBI guiding the fluid upwards and the temperature increase will happen from the upper part of the hide compartment HC to ensure no direct contact between high temperature stem and hide.

[0166] Accordingly, the temperature increasing fluid flow may be created by the first temperature regulation equipment 1TRE comprising a heating element HE heating up e.g. water so that a steam is created than can be introduced into the tanning drum. Theintroduction may as mentioned be controlled by the controller CON via control of one or more valves VA in a conduit system between the heater and the tanning drum. The controller may also control the heating element of the heating system.

[0167] The control of fluid flow and temperature of the fluid may e.g. be controlled based on a predetermined recipe requiring a certain temperature during a certain time period. This temperature may be provide to the controller via human machine interface from an operator or preset in a recipe automatically executed by the controller. As illustrated the controller CON receives a temperature feedback from a temperature sensor TES measuring the temperature inside the tanning drum TD. Note that the location of the temperature sensor in fig. 2 is only for illustrative purpose, it may preferably be located close to the center axis CA.

[0168] As mentioned the next step is a washing step WAS where the hides AH are washed to remove fibers. The washing step is a consequence of the dry tanning process where not water or very reduced amount of water is in the drum during the tanning step TAN and thus are not removed from the hides when the drum is drained.

[0169] The washing step WAS include attaching the hides AH to a hanger which is then dipping and / or dragging the hides through a washing container. During these movements through the water fibers are removed from the hides. As the fibers are now in the water, the water needs to be filtered or replaces often. The wash container WC of fig. 2 is illustrated with a conduit CO, filter FI and a pump PU which together ensure clean water for the washing of the hides.

[0170] With reference to fig. 3 an embodiment of a tanning system TS including process equipment PE for the tanning process is illustrated and will be explained in detail in the following. The process equipment PE for automatic or semiautomatic tanning of animal hides AH is schematically illustrated in fig. 3. Additionally, the tanning drum TD comprises air release valves ARV, to relieve pressure.

[0171] The process equipment PE includes a tanning drum TD that may be known from conventional tanning processes and such equipment could be a container or a drum, which may be a big-sized cylindric-shaped machine rotating horizontally around its center axis CA and is large enough to contain a plurality of hides such as several hundred animal hides that may weight several thousands of kilos. The tanning drum TD has at least one opening for the addition of animal hides and this opening or another opening may also be used for the addition of tanning agents to the animal hides in the tanning drum TD. The tanning drum TD may be a drum, that has an animal hide inlet ANI in the form of a hatch that may be opened to introduce the animal hides, a liquid such an aqueous solution and / or the tanning agent. The drum may be configured to retain the components used for the tanning process / tanning step TAN. The process equipment moreover includes a first temperature regulating equipment 1TRE and a second temperature regulating equipment 2TRE. This temperature regulating equipment establishing the intended temperature in the tanning drum under control of the temperature controller TEC. The temperature regulating equipment may typically include at least a heater and preferably also a cooler, or whatever may be appropriate to heat, optionally cool or at least setting the intended temperature of the content in the tanning container or streams injected into the tanning container.

[0172] In fig. 3 an auxiliary unit AUX is illustrated with an additional conduit ACO connected to the tanning drum TD in proximity of the center axis CA. This auxiliary unit AUX serves the purpose of illustrating that fluids for cooling or additional components relevant for the tanning step TAN or other steps of the tanning process may be included in the tanning system TS. Such auxiliary functions may e.g. be controlled manually or by the controller CON.

[0173] Hence, fluid may be added from a first source via a conduit CO or from a second source via an additional conduit ACO. This is advantageous in that fluid of two different temperatures and / or two different types can be introduced into the tanning drum. Accordingly, if temperature is to be increased fluid from one source may be introduced and if temperature is to be decreased, fluid from the second source may beintroduced. Flow of fluid from the two sources may be controlled by a plurality of valves and thus only one fluid inlet may be needed into the tanning drum for fluids from both sources. However, the tanning system may also in embodiments have one inlet per source.

[0174] More specific, the first temperature regulating equipment 1TRE is based on a heating element HE for heating a fluid supplied from a fluid source FS. The fluid may be water and the fluid source may be a vessel or a conduit supplying the heating element HE with water when needed. The heating element HE may be an electric heating element power from a not illustrated power source such as the utility grid.

[0175] The fluid source FS is fluidly connected to the heating element via a conduit CO and the heating element is fluidly connected to the tanning drum via a conduit CO. The temperature controller TEC may control the flow of fluid inside the conduits via valves VA and / or via the heating element HE. This control is based information of e.g. the animal hide AH and the current temperature inside the tanning drum. This temperature may be provided to the controller CON / temperature control TEC via a temperature sensor TES measuring temperature inside the tanning drum.

[0176] It should be mentioned that in an embodiment, the first temperature regulation equipment 1TRE may comprise a second fluid source (illustrated as the auxiliary unit AUX) or a conduit by-passing the heating element (not illustrated) or a cooling system (illustrated as the auxiliary unit AUX). Via one or more of these elements / configuration of elements, the temperature controller TEC may be able to also provide a cooling fluid into the tanning drum. Such cooling fluid may be the same fluid as the fluid used to heat the inside temperature of the tanning drum just not heated.

[0177] More specific, the second temperature regulating equipment 2TRE is based on a rotation of the tanning drum TD. This rotation creates a friction between the hides / between hides and drum wall because there is no or very little water in the drum. The rotation is controlled by a motor drive MOD such as variable frequency drive supplying an electrical motor EM with power. In this way based on input from thecontroller CON or from the temperature controller TEC, the rotational speed of the drum is controlled and the higher rotational speed, the higher heat is generated from the friction between the hides and between the hides and interior of the tanning drum.

[0178] The electric motor EM is mechanically connected to the drum e.g. via a mechanical drive MED such as a belt drive or via a toothed wheel transferring rotational force from the motor EM to the drum TD.

[0179] The tanning drum may be made of wood planking, steel or polypropylene or any material capable of withstanding deterioration of the material caused by the chemical agents used during the tanning process. An example of a tanning process equipment may e g. be a PPHTT NJ with AUTOMATIC DOOR PAB / 140 by the manufacturer Hiini.

[0180] The tanning process equipment PE may be arranged with different types of control equipment such as a time controller TIC controlling the during of time under which the process equipment works, e.g. duration of tanning cycles, rotations cycles / speed, heating cycles, etc., a temperature controller equipment TEC controlling the temperature in a tanning drum of the system. These controllers may all be implemented in a singular or distributed controller CON controlling the automatic operation of the tanning process equipment PE including the temperature inside the tanning drum.

[0181] The tanning process may be controlled based on process parameters. The process parameters relevant for executing the tanning process as controlled and monitored by the controller CON must be based on assumption, measurements or knowledge of certain important data, namely animal hide characteristics. The animal hide characteristics would typically include at least the type / origin of the hide, i.e. a determination or input to the controller defining whether the hides to be tanned are from cow, goat, kangaroo, yak, etc. The tanning process according to an embodiment of the invention depends on the type of animal hide AH to be introduced into the tanning drum. Different types of animal hide AH may be more or less loose, maycontain more of less collagen, etc., and this will have to be considered in connection with the control of the tanning process.

[0182] In principle, it may be important to include or apply test equipment to measure such characteristics and make the data available to the controller CON with little or no human interaction (e.g. calculations) or the characteristics may be determined manually, e.g. simply as skin types, and the relevant process parameters such as process duration, temperature setpoint or temperature development, rotational speed of the tanning drum, rotational direction etc may be input to the controller. Such processing routines may also be included and programmed into or in relation to the controller in order to present a number of preset programs available for the user to select based upon the animal hide characteristics.

[0183] A further animal hide characteristic which should be taken into consideration is the weight of the animal hides to be tanned in the tanning container. This weight may be determined manually in input into the controller by a human operator or it may be determined automatically run-time on the basis of data received from a weigh cell associated with the tanning drum.

[0184] Other animal hide characteristics may be applied within the scope of the invention, but the above is most often brought into use, some way, somehow.

[0185] As mentioned the inside temperature of the tanning drum TD may be adapted to be heated under control of the controller CON or temperature controller TEC which may be the same or separate controllers. The temperature control is important to increase the temperature inside the container to speed up the tanning process and / or to complete the tanning process by fixing of binding the tanning agent e.g. chrome tanning, Wet-Bright / Wet- White or vegetable tanning to the animal hide. The increase may be from approximately ambient temperature, approximately 20-22 degree Celsius (depending on winter- / summertime and geographic location of the tanning system TS), to between 30-50 degree Celsius depending on the required tanning temperature.

[0186] The measurements and control of the temperature during the tanning process / tanning step TAN according to embodiments of the invention, may be performed by any suitable temperature controller TEC configured for controlling temperature in the tanning drum through the tanning process. Such controller may work by measuring the temperature or receiving inputs representing such temperature e.g. from a temperature sensor TES measuring the temperature directly inside the tanning drum, and the controller may communicate relevant software control signals to the temperature regulating equipment such as motor / motor drive, valve, heating elements and / or cooler such as a fluid inlet in order to achieve a desired temperature in the tanning drum TD. The temperature may be measured by one or more temperature sensors TES measuring the temperature in the tanning drum or a derivative thereof and the sensors are communicatively coupled to the controller, thereby facilitating automatic control of tanning control parameters on the basis of the measured temperature values and of course optional further measured values and process parameters.

[0187] The time may also be preset and controlled during the tanning process. The time controller may be any suitable and programmable time controller and may be connected to the temperature regulating equipment TRE. Such connection may be mediated by a wire or may be wireless. The preset time may cover the total process or at least the duration of time until a first interruption of the tanning process at which e.g. pH is measured, where after the remaining process time may be determined or a time until next interruption is determined. The time controller may also be used to provide temperature set points to the controller CON which based on this input may change state of the tanning process. Such change of state may be from one part of a predetermined tanning program with one temperature for a specific period of time to another part of predetermined tanning program with another temperature.

[0188] The pH values may be measured by a pH meter or pH tracer which can be connected to the controller CON or they may be measured manually. Examples of pH meters used in the field of tanning could be a pH tracer (PHT)-ETP. The pH measuringmay include measuring of the pH in the additives or the combination of additives and hides in the tanning container.

[0189] If required, the pH of the animal hides is to be measured during the process, such pH measuring may typically be measured relatively manual, depending on how exact and how often such measurement is to be made.

[0190] pH may be controlled actively by e.g. the addition of base. An example hereof may be the addition of Feliderm MgO into the equipment, where the basification process may be run for e.g. 8 hours for the binding of tanning agent in the animal hides.

[0191] pH may also be controlled reactively by the use of a self-basifying tanning agent. An example hereof may be a self-basifying chrome sulphate, such as e.g. Baychrom A. By use of a self-basifying agent, there may be no need for an additional basifying agent, and the basifying may be obtained by increasing the heat inside the equipment.

[0192] In fact, any compound that can raise the pH of the tanning solution to a value higher than 3.5 can be considered as a candidate to be the basifying agent.

[0193] The control of pH may be run automatically or at least partially automatic by means of the controller CON. In other embodiments, such a control of pH may be effected by interrupting the tanning process or programming intervals at which pH measuring and optional supplementary pH control is performed. Such a process would typical by effected by an active control of pH as explained above.

[0194] The control of pH may also be run as a hybrid active and reactive process, e.g. by starting out with a self- basifying tanning agent including pH controlling agents and then subsequently during the tuning process tuning the pH by actively adding pH controlling agent, e.g. after measurement of pH in the drum and / or pH of the hides performed at intervals during the process.

[0195] The process is performed at atmospheric pressure, or optimally where the pressure inside the container is substantially similar to the pressure surrounding the container. Optionally the process may be performed in a non-pressurized container. This means that the pressure inside is maintained similar to that of the surrounding, without actively increasing it during the tanning process. However, it may be foreseen that an increase in temperature inside the tanning equipment may change the pressure inside the drum slightly. Also the introduction of a fluid for regulating the inside temperature may increase the pressure inside the drum. To compensate for such pressure increase, at least one drum end is equipped with air releasing valves ARV one of which may automatically open when moving upwards crossing the center axis. Preferably, an air release valve ARV is not opened before it has crossed the horizonal plane defined by the center axis CA.

[0196] Alternatively, the tanning equipment is not airtight or has a safety valve that opens if the pressure increases during the processes. If the pressure inside the container rises above 1.2-2 atmospheres it may be seen as hazardous, both to machinery and the operators working with the machinery.

[0197] According to embodiments of the invention, the drum may be a closed system during the tanning process. The drum may be understood as a container capable of holding the animal hide, any water and / or aqueous solution that is used for the tanning process and / or heating, any tanning agent that is introduced in dry, solid, liquid, wet or in any form, without changing the concentrations of the components inside the tanning equipment.

[0198] The process parameters may be determined based on an initially assessment of the animal hide characteristics AHC. Here, several parameters must be taken into account when setting such process parameters PP as there may be great variations of the starting point and consequently the process parameters for running an optimal tanning process resulting in a uniform distribution of tanning agents.

[0199] Such variations may be the weight and / or thickness e.g. of a lime split or full substance of the animal hides, where a thick and dense animal hide may need e.g. longer time, or a higher temperature compared to a thinner animal hide. Further, there are also great differences of the characteristics between the hides from different animals e.g. cattle and a crocodile, or even within the same race e.g. calf, veal, heavy veal, cow, bull, ox etc. Other variations of the starting point of the animal hides may also be if the animal hides are salted or not, how well dehydrated the animal hides are, how much hair and / or fat present on the hides, the amount of animal hides that are to be processed.

[0200] When the process parameters are determined, based on e.g. the above described examples of animal hide characteristics, the automatic tanning process or at least the tanning step TAN for tanning animal hides can be initiated and carried out at least partly automatic.

[0201] A tanning step TAN based on the animal hide characteristics is then set up e.g. as a manual for the operators of the tanning step TAN including specifications of e.g. selection and concentration of chemicals, temperature of eater inlet, running time, drum speed, rotation direction etc. Such tanning step TAN is setup to run automatically, however, control steps may be included during the process wherein e.g. pH is measured throughout the cross section of the animal hides to control if it is in the correct range. Such pH measure may be done by cutting the hide and measuring pH with a pH indicator of the cross section, e.g. layers as grain, middle and flesh to make sure there is an even pH distribution throughout the layers. The results during the control steps may then lead to a fixed direction for the next step. Powders may also be added manually to the process. Process control steps to check the pH of the cross section / layers indicators may be used where: Phenolphthalein <8,2 Colorless > 8,2 Pink and / or Broomcresol Green <3,8 Yellow > 5,4 Blue etc.

[0202] Fig. 4 illustrates two graphs related to a tanning step TAN according to the present invention. The upper graph illustrates the discontinued time periods during which fluid is injected into the tanning drum to regulate the inside temperature and theaccumulated amount of added fluid during the tanning step TAN. The lower graph illustrates the temperature inside the tanning drum as consequence of the injected fluid. As illustrated, in this example, the fluid is warmer than the inside temperature which is therefore increasing as consequence of the injection.

[0203] The graphs are only describing a theoretic tanning step to ease understanding of the principle of the invention. Depending on the specific type of hide to be tanned, number of hides in the tanning drum, volume of the tanning drum, ambient temperature, etc. the graphs will break away from the illustrated numbers but not form the illustrated principles.

[0204] The principle tanning step TAN described by the graphs has a duration of 18 hours as indicated along the X-axis of the two graphs. Also as illustrated at the upper graph, the percentage of water in the tanning drum is 100% at the start of the tanning step TAN. This mean that either the hides AH all have reached their maximum water retention capacity and there is no carryover water from a previous process. Alternative, there is some carryover water and the hides have not all reached their maximum water retention capacity. With this said the hides may all have reached their maximum water retention capacity of 100% and in addition, there may be an additional amount of carryover water corresponds to 10%-20% of weight of the soaked animal hides. Furthermore, a minimal amount dilution waters might be added.

[0205] Tanning agent is introduced via the animal hide inlet AHI which is subsequently closed, and the tanning step start at time 0. The tanning step TAN includes a fist part and a second part. During the first part (which may last for 4-12 hours), the tanning agent is distributed and dissolved in the drum during rotation of the drum TD. The temperature is substantially ambient temperature. During the second part (which may last 6-8 hours), the inside temperature is increased during rotation. The temperature increase is controlled e.g. in successive steps as described below.

[0206] As the drum starts rotating, the second temperature regulating equipment 2TRE start to impact the inside temperature and to ensure that the temperature doesnot increase to a point where the tanning agent is activated, the inside temperature may be reduced by injecting a cooling fluid into the drum. The rotation is, by the second temperature regulating equipment 2TRE, generating heat by friction between the hides / hides and drum wall. Surprisingly, this friction occurs because of the reduced liquid inside the tanning drum despite the fact that liquid may be present and that the hides may be soaked with the liquid.

[0207] As mentioned, only the second temperature regulating equipment 2TRE is generating heat during the first part i.e. in this example during the first 10 hours of the tanning step TAN. The heat impact from rotation during the first 10 hours is minimal e.g. due to a slow rotation of the drum, but for illustrative purpose the temperature curve on the lower graph is illustrated as increasing during these 10 hours. Hence, in this example, the ambient temperature may be 20C and the inside temperature of the tanning drum is increased by one degree to 21C after 10 hours.

[0208] After 10 hours, the first art of the tanning step TAN is over and the second part begins. Thus, fluid is injected into the tanning drum TD and the temperature starts to rise while the fluid is injected. Fluid is injected for 30 minutes, illustrated by the block of the upper graph, which make the temperature increase from 21C to 24C, illustrated at the lower graph. The temperature is maintained at 24 degrees for 30 minutes as this is required by the tanning recipe of this example. This may require nonillustrated injections of fluid between hour 10’A and hour 11.

[0209] The recipe then teach to increase the temperature to above 25C such as between 25C and 60C, such as between 25C and 45C, such as between 35C and 40C which is the desired range of temperatures for the rest of the tanning step TAN. Hence from hour 11 to 11 Vi fluid in the form of a steam of water is introduced to increase the temperature from 24C towards the desired tanning temperature which is this example is 31C.

[0210] As illustrated, this temperature is between an upper and a lower threshold temperature of 29C and 31C respectively which is an acceptable deviation from thedesired temperature of the tanning in this particular example. If the upper threshold is exceeded, fluid is injected having a temperature below 31C, preferably much below such as 10 degrees or lower (how much lower determine the amount of fluid needed to the reduce the temperature), to reduce the temperature inside the tanning drum.

[0211] The steam (of water in this example) is generated by the first temperature regulating equipment and together with the heat generated by the second temperature regulating equipment the inside temperature is increased. Hence, the illustrated temperature curve of the lower graph includes contributions from both the first and second temperature regulating equipment.

[0212] Over time when no fluid is injected, the temperature will drop in this example. The speed of this temperature decrease depends e.g. on ambient temperature, rotation speed (contribution from the second heater), etc. In this example, after hour 12, the temperature has dropped to the lower threshold i.e. to 29C. Therefore, steam is again introduced for a short period of time to get the temperature back up between the two thresholds. In this way, the temperature is, during the second part until hour 18 where the tanning step TAN is finished, regulated by discontinued introduction of steam into the tanning drum and / or by changing the rotation speed of the drum. These discontinued introductions of steam may only be of a few seconds such as e.g. 10 seconds e.g. 5 minutes interval in that the drum at this point is heated up and thus a thermal inertia is built up in the tanning drum construction. Thus, the temperature only needs to be maintained, nothing at this point in time needs to be heated from starting temperature at this point.

[0213] As mentioned, the temperature development is illustrated at the lower graph. From the upper graph the accumulated liquid in the tanning drum is illustrated. As can be found from this example, the total amount of liquid is 130% at the end of the tanning process. This include the 100% present at the beginning of the tanning process and then the 30% of this amount is introduced during the tanning process as part of the temperature control.

[0214] It should be noted that the temperature control might introduce more fluid than the 30% that is possible to determine inside the tanning drum after the tanning process is introduced. This is because part of the introduced steam escapes the tanning drum via the air release valves ARV as part of the automatic pressure balancing of the pressure inside the tanning drum.

[0215] Accordingly, in this example a total of 50% liquid by weight may be added during the tanning process, but only 30% is possible to determine at the end of the tanning step TAN. Note that this (either the total amount of added fluid or the part of the added fluid detectable in the drum at the end of the tanning step TAN) could in other examples be between 10% and 50% and note that all this or at least 50%, 40%, 30%, 20% or 10% of this added liquid may be added as steam of water. Also note that the way to determine amount of added liquid here is by weight of the hides including the water retained in the hides. Alternatively, the amount added liquid may be determined by weight of dry hides (pre or post the tanning process), measurable liquid surface inside the tanning drum, etc.

[0216] Thus, again with reference to this theoretic tanning example described above having a liquid and temperature increase as illustrated on the graphs of fig. 4, if the tanning process start with 100% water in the tanning drum (i.e. not more than what can be contained / retained by the hides), during the first 10 hours dilution fluid may be added such as up to 2% (calculated from the water retention capacity of the animal hides) together with chemicals such as fat liquors or fungicides. The fluid and chemicals may be added all at the same time or in portions over time. Accordingly, at hour 10 or 11 in this particular embodiment 2% fluid may be added making the total amount of fluid in the tanning drum 102%. More than 2% may be introduced during the following hours such as during hour 11, but as mentioned some of the steam escapes via the air release valves ARV. As a non-limiting example, the total amount of fluid introduced into the tanning drum may, after hour 13, be 7% making the total amount of liquid in the drum 107%. At the end of the tanning step TAN, 11% fluid may be added making the total amount of fluid in the drum 111% when the tanningstep TAN has ended. Hence, the temperature increase may start with inlet of water steam, the increase of water in the drum due to this may be negligible. If visible water is present in the drum when unloading hides this may be due to the fact that the drum was not drained sufficient after the pickle step i.e. such water may be carryover water from the pickle float.

[0217] It should be noted that, the fluid introduced in fig. 4 may be water and / or water steam and that, the amount of such fluid, may be based on the weight of the soaked animal hides.

[0218] Thus, that actual amount of fluid required from a fluid source is more than what can be determined after the tanning process i.e. more than the 11%. Due to the escape of steam via the air release valves ARV, the total amount of water introduced during the tanning step TAN may be 17% by weight of the hides including retained water at the start of the tanning process. In this example, maybe 6% escapes via the air release valves ARV and thus 11% remain in the tanning drum at the end of the tanning step.

[0219] One way of establishing the amount of added fluid is by comparing the weight of the tanning drum or content of the tanning drum both before and after the tanning step TAN. Alternatively, measure the liquid level inside the tanning drum (e.g. with respect to the center axis) both before and after the tanning step TAN. At least the latter method, may require a settling time after the tanning process for the fluid e.g. of the inner sides of the tanning drum to gather at the bottom of the tanning drum. As the weight of a gaseous fluid such as a water steam does not change when changing phase to liquid state, settling time may not always be needed. However, this may depend on the method of determining the weight of the content of the tanning drum.

[0220] Alternative, the amount of added fluid may be determined based on a measuring of the fluid source such as a tank, ambient air or a pipe supply. By knowing amount introduced to the first temperature regulating equipment 1TRE knowledge is also obtained regarding amount introduced to the tanning drum.

[0221] It should be noted that when determining the amount of introduced fluid during the tanning process, the introduction of tanning agent should be considered. One way of doing so is by comparing determining a start weight / height of liquid surface after the tanning agent is introduced into the tanning drum.

[0222] The weight of hides in a tanning drum with 100% water retained depends on the type of hides and can be established when there is no additional water in the drum such as no water surface.

[0223] Thus, in the above example, the amount of water introduced is limited and preferably at least partly in the form of steam. In this way the dosing of tanning agent is easier, the temperature control is more precis, the contribution from the second heating is increased and the heating is faster in that no thermal inertia has to be built up in a large amount of water inside the tanning drum.

[0224] The dosing of tanning agent may lead to a reduction of tanning chemicals is at least 5%, such as at least 10%, such as at least 15%, such as at least 20%, such as at least 25%, such as between 10-30%. Specifically with respect to chrome the reduction is at least 2%, such as at least 3%, such as at least 4%, such as at least 5%, such as at least 8%, such as between 2%-8%, such as between 4%-6%.List of reference signs:ADC. Additional ConduitAHI. Animal Hide InletARV Air release valveAUX. Auxiliary unitBAT. BatingCA. Center AxisCO. ConduitCON. ControllerCUR. CurringDEL. DelimingDES. DesaltingDYE. DyeingEM. Electric MotorFAT. FatliquoringFI. FilterFIN. FinishingFLE. FleshingFS. Fluid SourceHC. Hide CompartmentHE. Heating ElementLE. LeatherLIM. LimingMED. Mechanical DriveMOD. Motor DriveNEU. NeutralizationPE. ProcessPIC. PicklingPRET. PRE-Tanning stepsPOSTT. POST-Tanning steps PU. PumpRH. Raw HidesRET. RetanningSAM. SammyingSH. ShovelSHA. ShavedSPL. SplitTAN. TanningTD. Tanning DrumTEC. Temperature ControllerTES. Temperature SensorTIC. Time ControllerTS. Tanning SystemVA. ValveWAS. WashingWB. WashboardWBI. Washboard InletWC. Wash Container1TRE. First Temperature Regulating Equipment2TRE. Second Temperature Regulating Equipment

Claims

Patent Claims1. A method of regulating an inside temperature of a tanning drum, during a tanning step (TAN) of a tanning process of tanning a plurality of animal hides (AH), wherein said tanning drum (TD) comprises a center axis (CA), a mechanical drive (MED) and an animal hide inlet (AHI), wherein said mechanical drive (MED) is connected to an electric motor (EM), wherein said electric motor (EM) is configured to rotate said tanning drum (TD) via said mechanical drive (MED), wherein said method comprise the step of regulating said inside temperature at least partly by first temperature regulating equipment (1TRE) and / or at least partly by second temperature regulating equipment (2TRE), wherein said first temperature regulating equipment (1TRE) includes a heating element (HE), and wherein said second temperature regulating equipment (2TRE) includes said electric motor (EM) and said mechanical drive (MED) providing heat from rotation of said tanning drum when said tanning drum comprises said plurality of animal hides (AH).

2. A method according to claim 1, wherein said tanning step (TAN) is a dry tanning step (TAN).

3. A method according to claim 1 or 2, wherein said tanning drum (TD) further comprises a temperature sensor (TES).

4. A method according to any of the preceding claims, wherein said temperature regulation of said tanning step (TAN) is automatically controlled by a controller (CON) based on a temperature measured by said temperature sensor (TES).

5. A method according to any of the preceding claims, wherein said tanning drum (TD) further comprises at least one, preferably at least two, most preferably at least three air release valves (ARV).

6. A method according to any of the preceding claims, wherein said tanning drum comprises a fluid inlet valve (VA) controlling the inlet of fluid into said tanning drum (TD).

7. A method according to any of the preceding claims, wherein said tanning drum (TD) comprises a liquid content with no liquid surface inside said tanning drum (TD).

8. A method according to any of the preceding claims, wherein said tanning drum (TD) comprises a liquid content with a liquid surface inside said tanning drum (TD) during said tanning step which is below said center axis (CA).

9. A method according to claim 8, wherein a distance from the surface of said liquid to said center axis (CA) during standstill of said tanning drum (TD) is at least 25cm, preferably at least 50cm, most preferably at least 100cm.

10. A method according to any of the preceding claims, wherein said tanning drum (TD) comprises a liquid content less than 10%, 20%, 25%, 30%, 40%, 50% by weight of said plurality of animal hides (AH), when said plurality of animal hides (AH) are dry.

11. A method according to any of the preceding claims, wherein said tanning drum (TD) comprises a liquid content less than 10%, 20%, 25%, 30%, 40%, 50% by weight of said plurality of animal hides (AH) when said plurality of animal hides (AH) are soaked.

12. A method according to any of the preceding claims, wherein said tanning drum (TD) comprises a liquid content less than 110%, 120%, 130%, 140%, 150% of the liquid which is contained by said plurality of animal hides (AH).

13. A method according to any of the preceding claims, wherein an amount of added liquid during said tanning step is less than the amount of liquid present inside said tanning drum (TD) when starting said tanning step (TAN).

14. A method according to any of the preceding claims, wherein said plurality of animal hides (AH) comprises a liquid content according to the liquid retention capacity.

15. A method according to any of the preceding claims, wherein said plurality of animal hides (AH) comprises a water content exceeding the water retention capacity.

16. A method according to any of the preceding claims, wherein a fluid is added to the interior of said tanning drum (TD) during said tanning step (TAN).

17. A method according to any of the preceding claims, wherein said fluid is introduced into said tanning drum (TD) when said tanning drum (TD) is rotating.

18. A method according to any of the preceding claims, wherein said fluid is added from a first or from a second fluid source.

19. A method according to any of the preceding claims, wherein said fluid is a tanning liquid.

20. A method according to any of the preceding claims, wherein said fluid is steam, preferably water steam.

21. A method according to claim 20, wherein at least 50%, preferably at least 25%, most preferably at least 10% of the total injected fluid at the end of said tanning step origins from steam.

22. A method according to any of the preceding claims, wherein said fluid is introduced in discontinued time periods during said tanning step.

23. A method according to any of the preceding claims, wherein said discontinued time periods are present during a tanning part of said tanning step (TAN).

24. A method according to claim 23, wherein a first time period of said discontinued time periods is between 5 and 60 minutes, such as between 5 and 45 minutes, such as between 5 and 30 minutes.

25. A method according to claims 22 or 23, wherein a last time period of said discontinued time periods is between 1 second and 1 minute, preferably between 2 second and 30seconds, most preferably between 3 seconds and 15 seconds.

26. A method according to any of the preceding claims, wherein said introduction of fluid is continuously introduced alternatingly between a temperature maintaining flow and a temperature increasing flow.

27. A method according to any of the preceding claims, wherein said inside temperature is controlled to be between 20-55 degree Celsius.

28. A method according to any of the preceding claims, wherein said controller (CON) is decreasing said inside temperature by introducing said fluid when said fluid has a temperature which is below said measured temperature inside said tanning drum (TD).

29. A method according to any of the preceding claims, wherein said temperature of said fluid is controlled by a cooling system fluidly connected to said tanning drum (TD).

30. A method according to any of the preceding claims, wherein said fluid having a temperature below said measured temperature is introduced into said tanning drum (TD) in a separate conduit (CO).

31. A method according to any of the preceding claims, wherein said measured temperature inside said drum is controlled by a cooling system regulating a temperature of a cooling fluid circulated in a void between a second and a first wall of said drum.

32. A method according to any of the preceding claims, wherein said controller (CON) is increasing said inside temperature by introducing said fluid when said fluid has a temperature which is above said measured temperature inside said tanning drum (TD).

33. A method according to any of the preceding claims, wherein said fluid is introduced into a hide compartment (HC) of said tanning drum (TD) above said center axis.

34. A method according to any of the preceding claims, wherein said heating element (HE) is heating up said fluid outside of said tanning drum (TD) which fluid is subsequently introduced into said tanning drum (TD) via a conduit (CO).

35. A method according to any of the preceding claims, wherein said heated fluid is introduced into said tanning drum (TD) in gaseous form.

36. A method according to any of the preceding claims, wherein rotation of said tanning drum (TD) is control by said controller (CON) controlling frequency and voltage of power supply to said electric motor (EM).

37. A method according to any of the preceding claims, wherein an increase of the rotation speed of a motor axis of said electric motor (EM) is contributing to increasing said inside temperature of said tanning drum (TD).

38. A method according to any of the preceding claims, wherein said electric motor (EM) is a variable speed motor,39. A method according to any of the preceding claims, wherein said second temperature regulating equipment (2TRE) is provided when said liquid surface is less than 10cm from the bottom of said tanning drum (TD), such as less than 5cm from the bottom of said tanning drum (TD).

40. A method according to any of the preceding claims, wherein said automatically controlled temperature regulation comprises the following steps:during rotation of said tanning drum (TD), detect a current temperature inside the tanning drum (TD), if said current temperature is below a lower threshold temperature, inject a water steam into said tanning drum (TD) via said fluid inlet, to increase said current temperature, and if said current temperature is between said lower threshold temperature and a first upper threshold temperature, continue rotation of said tanning drum (TD) without injecting fluid into said tanning drum (TD).

41. A method according to any of the preceding claims, wherein said automatic control further comprises the step of if said current temperature is above a second upper threshold temperature, inject fluid into said tanning drum (TD) via said fluid inlet, to decrease said current temperature.

42. A method according to any of the preceding claims, wherein said fluid inlet is closed during detection of said current temperature.

43. A method according to any of the preceding claims, wherein said plurality of animal hides (AH) is washed in a washing process after said tanning step.

44. A method according to any of the preceding claims, wherein said washing process is carried out outside said tanning drum (TD) in a washing container (WC) comprising a fiber filtration filter.

45. A method according to any of the preceding claims, wherein said animal hide (AH) comprise bovine hide, cattle hide, cow hide, or calf hide.

46. A method according to any of the preceding claims, wherein pressure inside said tanning drum (TD) during said tanning process is within a range of 0.7-1.3 atmospheric pressure such as 0.9-1.1 atmospheric pressure.

47. An animal hide tanning system (TS) configured for tanning a plurality of animal hides (AH), said tanning system (TS) comprising:- a tanning drum (TD), said tanning drum (TD) comprising a center axis (CA), a mechanical drive (MED) and an animal hide inlet (AHI), wherein said mechanical drive (MED) is connected to an electric motor (EM), wherein said electric motor (EM) is configured to rotate said tanning drum (TD) via said mechanical drive (MED),- a temperature control system, said temperature control system comprises a temperature sensor (TES), a first temperature regulating equipment (1TRE), a second temperature regulating equipment (2TRE) and a temperature controller (TEC), wherein said temperature controller (TEC) is configured for regulating an inside temperature of said tanning drum (TD), during a process of tanning a plurality of animal hides (AH) by regulating said inside temperature at least partly by said first temperature regulating equipment (1TRE) and / or at least partly by said second temperature regulating equipment (2TRE), wherein said first temperature regulating equipment (1TRE) comprises a heating element, and wherein said second temperature regulating equipment (2TRE) comprises said tanning drum (TD) comprising said plurality of animal hides and configured for being rotated.

48. A system according to claim 47, wherein said tanning system further comprises a cooling system configured for cooing a fluid wherein said cooling is configured for being introduced into said tanning drum (TD) via a conduit (CO).

49. A system according to claims 47 or 48, wherein said fluid is introduced in discontinued time periods during said tanning step.

50. A system according to claim 49, wherein said discontinued time periods are present during a tanning part of said tanning step (TAN).

51. A system according to claims 49 or 50, wherein a first time period of said discontinued time periods is between 5 and 60 minutes, such as between 5 and 45 minutes, such as between 5 and 30 minutes.

52. A system according to any of the claims 47-51 regulating the inside temperature of said tanning drum according to the method of any of the claims 1-46.

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